Li-exchanged low silica EMT-containing metallosilicates

ABSTRACT

The present invention is a composition, a synthesis of the composition and a method of using the composition for selectively adsorptively separating nitrogen from oxygen wherein the composition is a crystalline EMT with a Si/Al ratio less than 2.0 and a lithium cation exchange of at least 80%, preferably including an intergrowth with a crystalline FAU structure, wherein the pure or intergrowth compositions have the chemical formula: 
     
         (0.2-0.0)M.sub.2/n 0:(0.80-1.0)Li.sub.2 0:X.sub.2 0.sub.3 :(2.0 to 
    
      &lt;4.0)SiO 2   
     wherein M=a metal cation other than lithium having a valence of n, and X is selected from the group consisting of aluminum, gallium and boron, preferably aluminum.

This is a division of application Ser. No. 08/241,880 May 12, 1994.

FIELD OF THE INVENTION

The present invention is directed to the field of synthetic zeolites ofthe structure EMT and FAU/EMT. More specifically, the present inventionis directed to an intergrowth of cubic and hexagonal FAU/EMT crystals.The synthesis of the composition and use in adsorptive separations isalso demonstrated.

BACKGROUND OF THE PRIOR ART

Both natural and synthetic crystalline aluminosilicates are known andmay generally be described as alumino-silicates of ordered internalstructure having the following general formula:

    M.sub.2/n 0:Al.sub.2 0.sub.3 : YSiO.sub.2 :ZH.sub.2 O

where M is a cation, n is its valence, Y the moles of silica, and Z themoles of the water of hydration.

When water of hydration is removed from the crystallinealuminosilicates, highly porous crystalline bodies are formed whichcontain extremely large adsorption areas inside each crystal. Cavitiesin the crystal structure lead to internal pores and form aninterconnecting network of passages. The size of the pores issubstantially constant, and this property has led to the use ofcrystalline aluminosilicates for the separation of materials accordingto molecular size or shape. For this reason, the crystallinealuminosilicates have sometimes been referred to as molecular sieves.

The crystalline structure of such molecular sieves consists basically ofthree-dimensional frameworks of SiO₄ and AlO₄ tetrahedra. Isomorphoussubstitution of boron or gallium for aluminum in a zeolite framework maybe achieved. The tetrahedra are cross-linked by the sharing of oxygenatoms, and the electrovalence of the tetrahedra containing aluminum isbalanced by the inclusion in the crystal of a cation, e.g., alkali metalor alkaline earth metal ions or other cationic metals and variouscombinations thereof. These cations are generally readily replaced byconventional ion-exchange techniques.

The spaces in the crystals between the tetrahedra ordinarily areoccupied by water. When the crystals are treated to remove the water,the spaces remaining are available for adsorption of other molecules ofa size and shape which permits their entry into the pores of thestructure.

Molecular sieves have found application in a variety of processes whichinclude ion exchange, selective adsorption and separation of compoundshaving different molecular dimensions such as hydrocarbon isomers, andthe catalytic conversion of organic materials, especially catalyticcracking processes.

U.S. Pat. No. 3,123,441 discloses a lithium aluminum silicate zeolitehaving a lithium oxide to alumina ratio of 1:1 and a silica to aluminaratio of 2:1.

U.S. Pat. No. 3,411,874 discloses the preparation of a zeolite ZSM-2which has the chemical formula M_(2/n) 0:Al₂ O₃ :(3.3-4.0)SiO₂ :ZH₂ O.The composition includes lithium as the M specie and is known to haveutility for selective adsorption and separation of compounds, such ashydrocarbon isomers. The zeolite is synthesized from a single mixtureover a period of from three days up to three months.

In U.S. Pat. No. 3,415,736, lithium-containing crystallinealuminosilicate compositions are disclosed which are broadly recited toinclude (0.05-0.8)Li₂ O:(0.95-0.2)Na₂ O:Al₂ O(2.0-6)SiO₂ :(0-9)H₂ O and,m specifically, (0.3-0.8)Li₂ O:(0.7-0.2)Na₂ O. Al₂ O₃ :(2.8-4)SiO₂ :(0-9)H₂ O. These zeolites are known as ZSM-3. They also are described ashaving utility in selective adsorptive separations, such as forhydrocarbon isomers. The crystalline ZSM-3 is recited to contain ahexagonal crystalline structure. The zeolite is typically synthesizedfrom a combination of four solutions which form a gel from which thezeolite crystallizes over a period of hours or days.

In an article entitled, "Synthesis and Characterization of VPI-6" byMark E. Davis, appearing in Molecular Sieves, (1992) pp 60-69, acrystalline zeolite having cubic and hexagonal intergrowth in thefaujasite structure is disclosed. The synthesis of the zeolite involveaging a solution for 24 hours and indicates that aging is an importantcriteria of the synthesis. Specifically, the author of this articleattempted to synthesize the zeolite in only the sodium cation form. Theutility of the VPI-6 zeolite is recited to be as an adsorbent or ionexchange medium.

J. L. Lievens, et al. in an article "Cation Site Energies in DehydratedHexagonal Faujasite", appearing in ZEOLITES, 1992, vol. 12, July/August,pp 698-705, reviews properties of hexagonal faujasite designated as EMT.FAU/EMT intergrowths were also discerned in the studied EMT materials.Sodium was the cation which was involved in the cation site studies, andSi/Al ratios of 4.6 were specified.

U.S. Pat. No. 5,098,686 discloses faujasite compositions in which highSi/Al ratios are attempted, preferably above 3. Hexagonal and cubicstructure mixtures are disclosed. All of the examples have compositionswith Si/Al ratios above 3.7.

U.S. Pat. No. 5,116,590 discloses a zeolitic structure, ECR-35, whichhas a Si/Al ratio of 2:1 to 12:1, preferably 4. ECR-35 is an intergrowthof faujasite and Breck Structure Six (a nomenclature for hexagonalfaujasite, subsequently EMT). Cation sites are occupied bytetraethylammonium and methyltriethylammonium cations.

J. A. Martens, et al. in an article entitled "Phase Discrimination with²⁹ Si MAS MNR in EMT/FAU Zeolite Intergrowths", J. Phys. Chem. 1993, 97,pp 5132-5135, describes the evaluation of ZSM-2 and ZSM-3 in lithiumexchanged format to determine the content and extent of any EMT and FAUphases in their crystal structures.

G. T. Kokotailo, et al., reported in "Synthesis and Structural Featuresof Zeolite ZSM-3", Molecular Sieve Zeolites--I, Amer. Chem, Soc., 1971,pp 109-121, the synthesis of ZSM-3 with a composition of (0.05-0.8)Li₂O:(0.2-0.95)Na₂ O:Al₂ O₃ : (2-6)SiO₂ :(0-9)H₂ O.

D. E. W. Vaughan, et al., in "Synthesis and Characterization of ZeoliteZSM-20", in Zeolite Synthesis, Amer. Chem. Soc. 1989, pp 545-559,investigated the effect of potassium on the ZSM-20 material which wassynthesized with a template cation and reported to have hexagonal andcubic crystal structure. As reported in Table 1, potassium had anadverse impact on the formation of the ZSM-20 structure.

The prior art fails to provide a composition that is both lithium cationrich and aluminum rich which produces a cubic/hexagonal intergrowth ofFAU and EMT crystalline metallosilicate having significant adsorptionutility, such as air separation. The present invention as set forthbelow uniquely achieves these goals to provide a high performance,novel, nitrogen-selective gas separation adsorbent.

BRIEF SUMMARY OF THE INVENTION

The present invention is a crystalline metallosilicate compositioncomprising an EMT structure with a Si/X ratio of less than 2.0 and alithium cation exchange of more than 80%, wherein X is selected from thegroup consisting of aluminum, boron and gallium.

Preferably, the EMT structure is in an intergrowth with a FAU crystalline structure.

Preferably, the intergrowth has an EMT structure content in the range ofat least 5% to less than 100% by weight. More preferably, theintergrowth has at least 20% by weight of an EMT structure. Morepreferably, the intergrowth has at least 42% by weight of an EMTstructure.

Preferably, X is aluminum.

Preferably, the cation exchange of lithium is greater than 85%. Morepreferably, a remaining cation is selected from the group consisting ofcalcium, magnesium, zinc, nickel, manganese, sodium, potassium andmixtures thereof.

Preferably, the composition is approximately 2.0 Si/Al. More preferably,the composition is approximately 1.0 Si/Al.

Preferably, the composition is prepared from at least one aged gel.

In a preferred embodiment, the present invention is a crystallinealuminosilicate composition comprising an FAU/EMT intergrowth structurewith a Si/Al ratio of less than 1.4 and a lithium cation exchange ofmore than 80%.

The present invention is also a method of synthesizing a crystallinemetallosilicate composition having an intergrowth of EMT and FAUstructures, comprising; forming a first gel containing M_(2/n) O, Al₂O₃, ≧1.5 SiO₂ in water wherein M is a metal cation, ageing the first gelat a temperature below the crystallization temperature of itsconstituents, forming a second gel containing M_(2/n) O, Al₂ O₃, SiO₂ inwater wherein M is a metal cation, mixing the first gel and the secondgel, crystallizing the intergrowth of EMT and FAU structures andrecovering it from the mixture of the first and second gels, and ionexchanging the crystallized metallosilicate composition with a source oflithium.

Preferably, lithium is ion exchanged to greater than 80%.

Preferably, the mixture of the first gel and the second gel is heated toinduce crystallization.

Preferably, the source of lithium is lithium chloride.

Preferably, both gels are aged prior to mixing the gels.

Preferably, a gel is aged for a period of time in the range of 2 to 144hours at a temperature below the crystallization of the gel'sconstituents.

The present invention is also a process of adsorptively separating amore strongly adsorbed gas from a less strongly adsorbed gas in a gasmixture containing a more strongly adsorbed gas and a less stronglyadsorbed gas, comprising; contacting the gas mixture with a zone ofadsorbent containing crystalline metallosilicate composition having anEMT structure with a Si/X ratio of less than 2.0 and a lithium cationexchange of more than 80%, wherein X is selected from the groupconsisting of aluminum, boron and gallium, selectively adsorbing themore strongly adsorbed gas preferentially to the less strongly adsorbedgas, removing a gas containing the less strongly adsorbed gas anddepleted in the more strongly adsorbed gas from the zone and separatelyremoving the more strongly adsorbed gas from the adsorbent.

Preferably, the zone is operated through a series of steps in a cyclicalmanner comprising; adsorption where the gas mixture contacts the zone atelevated pressure to adsorb the more strongly adsorbed gas until theadsorbent approaches saturation with the more strongly adsorbed gas andthe gas containing the less strongly adsorbed gas and depleted in themore strongly adsorbed gas is removed as a product, discontinuingadsorption and desorbing the zone to remove adsorbed more stronglyadsorbed gas from the adsorbent to regenerate the adsorbent,repressurizing the zone with a gas rich in the less strongly adsorbedgas, and repeating the series of steps to conduct a continuous process.

Preferably, the steps are conducted in a plurality of parallel connectedadsorption beds as the zone wherein when one bed is conducting anadsorption step another bed is being regenerated. More preferably, theplurality of beds is two parallel connected beds.

Preferably, the more strongly adsorbed gas is nitrogen.

Preferably, the less strongly adsorbed gas is oxygen.

Preferably, the gas mixture is air.

Preferably, the adsorption is conducted at a pressure in the range of 10to 30 psia.

Preferably, the desorption is conducted at a pressure in the range of0.1 to 7 psia.

Preferably, the gas containing the less strongly adsorbed gas anddepleted in the more strongly adsorbed gas is at least 90% oxygen byvolume. More preferably, the gas containing the less strongly adsorbedgas and depleted in the more strongly adsorbed gas is at least 93%oxygen by volume.

Preferably, a remaining cation is selected from the group consisting ofcalcium, magnesium, zinc, nickel, manganese, sodium, potassium andmixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an x-ray diffraction (XRD) pattern graphing degrees (2θ) vs.relative intensity (counts) of the FAU/EMT composition of Example 1.

FIG. 2 is an XRD pattern graphing degrees (2θ)) vs. relative intensity(counts) of the FAU/EMT composition of Example 3.

FIG. 3 is an XRD pattern graphing degrees (2θ) vs. relative intensity(counts) of the FAU/EMT composition of Example 5.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to crystalline metallosilicatecomposition having an EMT structure having the chemical composition:

    (0.0 to <0.20)M.sub.2/n O:(>0.80 to 1.0)Li.sub.2 O:X.sub.2 O.sub.3 : (2.0 to <4.0)SiO.sub.2

wherein M equals a metal cation other than lithium having a valence of nand X selected from the group consisting of aluminum, gallium and boron.Preferably, the X constitutes aluminum. Preferably, the predominantcation is lithium with a remaining cation content being calcium,magnesium, zinc, nickel, manganese, sodium, potassium or mixturesthereof. Although the lithium cation exchange level can be anywhere fromgreater than 80 (Li/X ratio of more than 0.8) up to 100%, preferably theexchange is as high as possible, preferably a level of 85%+lithium isachieved. Although the silicon dioxide to aluminum oxide ratio is in therange of 2:1 to <4.0:1 (Si/Al=1 to <2.0), the preferred compositionalratio approximates 2.0 (Si/Al: 1).

The compositions of the present invention also include an intergrowthwith a metallosilicate FAU structure and can comprise the cubic FAUstructure (faujasite) intergrown with a hexagonal EMT structure(hexagonal faujasite) in a zeolitic crystal. The FAU/EMT crystallinezeolites of the present invention are a modified faujasite wherein thecubic faujasite is identified with the structure code FAU with its cubicstructure and silicon dioxide to aluminum oxide ratios in the range of2:1-4.0:1, making it a synthetic faujasite. A related structure withhexagonal symmetry is generally recognized under the code EMT. EMT andFAU are recognized zeolitic crystal structures of the StructureCommission of the International Zeolite Association, as set forth atpages 88 and 96 of the ATLAS OF ZEOLITE STRUCTURE TYPES, by W. M. Meierand D. H. Olson (1992) published by Butterworth-Heinemann on behalf ofthe Commission.

An important aspect in obtaining the intergrowth compositions of thepresent invention is the synthesis method using a combination of gels inwhich at least one gel has been allowed to age prior to admixture of thegels, preferably a silica-rich gel with a Si/Al>1.5, and inducingcrystallization of the desired crystalline zeolite, in this case, theFAU/EMT structures. The Synthesis mixture may contain at least twocations selected from sodium, lithium, tetramethylammonium, andpotassium. Alternatively, lithium exchange of the cation content of themetallosilicates of the present invention may be conducted aftercrystallization. Preferably, the synthesis is performed with two gels inwhich an aluminum-rich gel is mixed with a silicon-rich gel to producethe modified metallosilicates of the present invention.

Ageing of a gel for the purpose of this invention is the process ofpreparing a gel and maintaining it at a temperature below itscrystallization point for sufficient time so that when it is mixed withanother gel an intergrowth is ultimately formed under conditions ofcrystallization. Typically, the ageing period is from 2 hours up to andpotentially exceeding 6 days (144 hrs.). In the process of ageing a gel,the time necessary is approximately inversely proportional to the ageingtemperature.

The present invention will now be exemplified by specific examples setforth below:

Example 1. Crystallization of FAU/EMT involving the combination of twoaged precursor gels.

Gel `A` used in this preparation has a composition that is typical forthe synthesis of low silica X zeolite, e.g., such as disclosed inexample 18 of UK Pat. 1,580,928 (1977). It was prepared as follows. 3.33g of NaOH (Merck) is dissolved in 3.33 g of water. 5.0 g of Al(OH)₃(Merck) is added to obtain a solution of sodium aluminate. 6.23 g of 85%KOH (Merck) and 13.3 g of 50 wt. % NaOH solution are combined and addedto 20 g of water. The obtained sodium and potassium solution is added tothe sodium aluminate solution under stirring. A solution containing 12.2g of water glass (Merck) and 24.4 g of H₂ O is added. The obtained gelhas a molar composition: (Na₂ O )₄.34 (K₂ O)₁.45 (Al₂ O₃) (SiO₂)₁.8 (H₂O)₁₁₆. The gel A is aged at 40° C. for 42 hours.

Gel `B` was synthesized according to the procedure outlined for thesynthesis of ZSM-3 in Example 2, and per U.S. Pat. No. 3,415,736. It washeated during 6 h at 60° C. After this treatment, no crystalline phasesare present that are detectable with XRD. One third of gel B was mixedwith aged gel A, so that the OH/SiO₂ ratio in the mixture was 2.8. Theslurry was heated to 60° C. during 24 h to provoke crystallization. Thecrystallization product was recovered by centrifugation at 4,000 rpm andwashed until the pH of the wash water was below a value of 10. Thecrystallization product was a FAU/EMT intergrowth, characterized by theXRD pattern shown in FIG. 1 and the hexagonal platelet morphology foundby SEM. The zeolite has a Si/Al ratio of 1.18. Phase discriminationusing ²⁹ Si MAS NMR leads to conclude that the FAU/EMT intergrowth iscomposed of 32% of EMT phase, with Si/Al ratio of 1.21, and 68% of FAUphase, with Si/Al ratio of 1.15.

Example 2. Crystallization of FAU/EMT involving the combination of twoaged gels and both inorganic and organic cations.

Gel `A` was prepared as disclosed in Example 1 (low silica X type) andaged at 40° C. during 70 h.

Gel `B` was prepared following a recipe that is typical for thesynthesis of EMC-2, a siliceous EMT phase (M. J. Annen, D. Young, J. P.Arhancet, M. E. Davis and S. Schramm, Zeolites, 1991, 11, 98). To 26.2 gof H₂ O are added under stirring, 2.69 g of sodium aluminate (Hopkin &Williams), 2.2 g of 50 wt. % NaOH (Merck), 2.95 g of 18-crown-6-ether(Janssen) and 6.69 g of SiO₂ (Riedel de Ha en). The obtained gel B has amolar composition: (Na₂ O)₂.4 (18-crown-6-ether) (Al₂ O₃) (SiO₂)₁₀ (H₂O)₁₄₀ corresponding to an OH/SiO₂ ratio of 0.5.

Gel B is aged at room temperature for 46 hours before mixing it withaged gel A. The final mixture has an OH/SiO₂ ratio of 2.5. The synthesismixture is crystallized at 90° C. for 71 hours. The product is recoveredby centrifugation at 4,000 rpm and washed till the pH of the wash waterwas between 9 and 10. The sample is identified by XRD as a FAU/EMTzeolite. The EMT content determined with ²⁹ Si MAS NMR amounts to 20%.The FAU and EMT parts of the crystals have a Si/Al ratio equal to 1.21.

Example 3. Synthesis of FAU/EMT involving the use of one aged gel, inpresence of a mixture of an alkali metal cation (sodium) and atetraalkylammonium cation (tetramethylammonium).

An amount of 5 g of sodium aluminate (Hopkin & Williams) and 2.4 gsodium hydroxide (Merck) are dissolved in 20.2 g water. An amount of12.5 g of tetramethylammonium hydroxide pentahydrate (Aldrich) is addedunder stirring. When the solution becomes clear, 11.8 g of water glass(Merck) is added. The composition of the synthesis mixture expressed inmolar ratios of oxides corresponds to: (Na₂ O)₃.35 (TMA₂ O)₁.65 (Al₂O₃)(SiO₂)₂.5 (H₂ O)₉₅.

The OH/SiO₂ ratio of this synthesis mixture is 4.0. The mixture isstirred during 24 h at room temperature and subsequently crystallized ina closed polypropylene bottle at 80° C. during 2 h. The product isrecovered by centrifugation at 4,000 rpm and washed with distilled wateruntil the pH of the wash water is below a value of 10. Thecrystallization product is identified as a FAU/EMT intergrowth,characterized by the XRD pattern shown in FIG. 2. The zeolite has a SiO₂/Al₂ O₃ ratio of 2.1. Phase discrimination using ²⁹ Si MAS NMR,according to the method by Martens et al. (J. Phys. Chem. 1993, 97,5132) leads to conclude that the zeolite product is composed of 32% ofEMT phase, with Si/Al ratio of 1.07, and 68% of FAU phase, with Si/Alratio of 1.04.

Example 4. Crystallization of FAU/EMT involving the combination of anaged LSX gel and a slurry of crystals of a siliceous FAU/EMTintergrowth.

Gel `A` was prepared as described in Example 1.

The siliceous FAU/EMT crystals used as precursors in this synthesis ofFAU/EMT are of the ZSM-3 type. The detailed synthesis recipe is derivedfrom literature (J. Perez-Pariente, V. Fornes, J. A. Martens and P. A.Jacobs, Stud. Surf. Sci. Catal. 37, 1988, pp. 123-131). Acrystallization directing agent (CDA) is prepared from 16.3 g of sodiumhydroxide (Merck), 2.40 g sodium aluminate (Hopkin & Williams) and 32.85g of water glass (Merck). The molar composition of the CDA is: (Na₂ O)₂₆(Al₂ O₃) (SiO₂)₁₅ (H₂ O)₁₄₃.

The CDA is aged at 60° C. for 30 minutes before it is added to asolution containing 131.5 g of water glass (Merck) and 110 g of water.Additional aluminum is added as 18.65 g of AlCl₃.6H₂ O dissolved in 340g of water. After heating the slurry at a temperature of 90° C. for 1 h,the slurry is filtered to remove the excess of sodium silicate. Thefiltered cake is dried at 100° C. for 3 h, and then mixed well with 100g of water and filtered, mixed with 200 g of H₂ O and filtered again.7.80 g of LiOH:H₂ O (Janssen) is dissolved in 6.25 g of water. Thefilter cake is slurried in the lithium hydroxide solution. The OH/SiO₂ratio in the final synthesis mixture is 1.0. The crystallization isperformed at 60° C. for 50 hours. Based on XRD, the product isidentified as a FAU/EMT intergrowth. The XRD pattern is composed of acombination of broad and sharp diffraction lines, typical for ZSM-3. TheSi/Al ratio of the zeolite is 1.75. Based on ²⁹ Si MAS NMR, the FAUcontent is 57% with SiO₂ /Al₂ O₃ ratio of 1.64, and 43% EMT with a SiO₂/Al₂ O₃ ratio of 1.87.

One third of the slurry of ZSM-3 crystals in their mother liquor wasmixed with the aged gel A. The OH/SiO₂ ratio in the resulting mixturewas 2.8. The slurry was heated to 80° C. during 6 h. The solid productswere recovered by centrifugation at 4,000 rpm and washed until the pH ofthe wash water was below a value of 10. The product was essentially aFAU/EMT intergrowth, contaminated with a trace amount of gismondine, asderived from an XRD pattern. The zeolite has a Si/Al ratio of 1.3. Phasediscrimination using ²⁹ Si MAS NMR leads to conclude that the FAU/EMTintergrowth is composed of 42% of EMT phase, with Si/Al ratio of 1.35,and 58% of FAU phase, with Si/Al ratio of 1.25.

Example 5. Combination of aged gel and siliceous crystalline product.

The gel `A` and the slurry of siliceous FAU/EMT intergrowth crystalswere prepared in the way and quantities explained in Example 4. Theaging of gel A was performed at 40° C. for 69 h. ZSM-3 was crystallizedat 60° C. for 47 h. Aged gel A and one fifth of the slurry of ZSM-3crystals in their mother liquor were combined. The resulting mixture hasan OH/SiO₂ ratio of 3.4. The mixture was heated at 60° C. during 6 h toprovoke crystallization. The solid products were recovered bycentrifugation at 4,000 rpm and washed until the pH of the wash waterwas below a value of 10. The product was a FAU/EMT intergrowth,characterized by the XRD pattern shown in FIG. 3 and having the typicalplatelet morphology consisting of clusters of submicron hexagonalplatelets. The zeolite has a Si/Al ratio of 1.25. Phase discriminationusing ²⁹ Si MAS NMR leads to conclude that the FAU/EMT intergrowth iscomposed of 36% of EMT phase, with Si/Al ratio of 1.31, and 64% of FAUphase, with Si/Al ratio of 1.22.

Example 6. Synthesis procedure for Si/Al=1.1 material from a single agedgel.

NaOH was dissolved in deionized water (1.76 g NaOH/30.2 g H₂ O). Thesolution was cooled to 22° C. and 5.55 g of NaAlO₂ (ground sodiumaluminate, MCB, Lot SX274) were added and mixed for 20 minutes. Themixture was filtered and put in a polyethylene bottle outfitted with amagnetic stirrer bar. Na₂ SiO₃ (11.68 g) (sodium silicate) was addedgradually to the stirred solution. The bottle was capped and the mixturewas aged for 48 hours at 22° C. with stirring. After aging, the mixturewas crystallized at 80° C. for 2 hours. The product was filtered hotusing a Buchner funnel and air dried. The product's XRD pattern shows itto be an FAU/EMT intergrowth.

Lithium chloride solution (50 cc of 1.0M LiCl/g zeolite) was added tothe solid and heated at 95° C. for 4 hours. The mixture was filteredhot, and the solid was washed with 100 mL of deionized water. Theexchange and wash procedure was repeated 5 times. After the finalexchange and washing with 200 mL of deionized water, the product wasfiltered and air dried overnight.

Example 7. Synthesis procedure for intergrowth with Si/Al=1.4 from asingle aged gel.

NaOH (6.52 g) was dissolved in 20.0 g deionized water in a 60 mlpolyethylene bottle. Al(OH)₃ (4.40 g) was added and the mixture wasstirred until a clear solution was obtained (20 minutes). N-brand silica(from PQ Corp.) (20.07 g) was added to the stirred solution, which wascapped and aged with stirring for 24 hours. The mixture was thencrystallized for 2 hours at 80° C. The product was filtered hot and airdried. The product's XRD pattern shows it to be an FAU/EMT intergrowth.It was exchanged into the lithium ion form as described in Example 6.

Example 8. Crystallization of FAU/EMT involving the combination of twoaged precursor gels.

The preparation of gel `C` was based on a recipe for preparing lowsilica X zeolite reported in literature (G. Kuhl, Zeolites, 7 (1987)451-457), Gel `C` was prepared as follows. 8 g of NaOH (Merck) and 6.12g of 85% KOH (Merck) are dissolved into 44.1 g of water. Subsequently,4.85 g of sodium aluminate are added and the mixture stirred until aclear solution is obtained. 12.3 g of water glass are added and themixture stirred for 10 minutes. The resulting gel `C` has a molarcomposition corresponding to the following oxide ratio's: (Na₂ O)₅.3 (K₂O)₁.8 (Al₂ O₃) (SiO₂)₂.2 (H₂ O)₁.22.

The OH/SiO₂ ratio in gel `C` is 6.3. Gel `B` was prepared as explainedin Example 2 and heated at 60° C. for 6 hours. One fourth of gel `B` wasmixed with gel `C`. The OH/SiO₂ ratio was 3.0. This final mixture wascrystallized at 60° C. for 24 hours. The product was recovered bycentrifugation at 4,000 rpm and washing until the pH of the wash waterwas below a value of 10. The product was dried at 60° C. The product isidentified by XRD as a FAU/EMT intergrowth.

Example 9 Synthesis of FAU/EMT Intergrowth with Si/Al=1.17 with Two AgedGels.

Synthesis of FAU/EMT intergrowths involved two gels with different Si/Alratios.

Gel `1` was prepared as follows. 12.78 g of NaOH solution (50 wt. %) wasmixed with 49.2 g of deionized water. 6.66 g of Al(OH)₃ powder (J. T.Baker) was added to form a sodium aluminate solution. 50.0 g ofcolloidal silica (Ludox HS40, Dupont) was mixed into the above solution.The mixture was stirred at room temperature for 46 hours. The obtainedgel `1` has the following molar composition: Na₂ OAl₂ O₃ :10SiO₂ :140H₂O.sub..

Gel `2` was prepared as follows. 11.46 g of NaOH (97 wt. %) wasdissolved in 50.0 g of deionized water. 6.0 g of Al(OH)₃ powder (J. T.Baker) was added to form a sodium aluminate solution. 6.93 g of KOH(87.4 wt. %) was dissolved into the above solution. Then, 13.8 g ofsodium silicate (PQ "N" brand) was added to form a gel. The gel was agedat room temperature for 20 hours. The obtained gel `2` has the followingmolar composition: 5.3 Na₂ O:1.8 K₂ O:Al₂ O₃ :2.2 SiO₂ :122 H₂ O.

Gel `2` was combined with 1/8 of gel `1` to form a mixture. The mixturewas heated at 60° C. for 70 hours. The formed product was filtered andwashed. The crystalline product has an FAU/EMT intergrowth structure,characterized by its XRD pattern. Chemical analysis shows that thezeolite has a Si/Al ratio of 1.17. Example 9 shows that an FAU/EMTintergrowth can be synthesized without a template, crystallizationdirecting agent or a cation other than sodium and/or potassium.

Example 10.

The compositions from Examples 1 to 5 were exchanged into the lithiumform using five static batch exchanges with 50 cc 2M LiCl/g at 100° C.In all cases over 854 Li exchange was achieved.

Table 1 summarizes the characterization data and N₂ adsorption at 23°C., i arm for the compositions described in Examples 1 to 7 and comparesit to a LiX control. All the samples have at least 20% EMT present. Thedata clearly shows that the N₂ capacity is not adversely affected by thepresence of EMT and in Examples 1, 2, and 5 display N₂ capacitiessimilar to LiX not having EMT present at all.

                  TABLE 1                                                         ______________________________________                                        Characterization and nitrogen adsorption for Li-exchanged                     FAU/EMT intergrowths.                                                                           EMT               N.sub.2 Capacity                                            Content   Micropore                                                                             23° C., 1 atm                      Example  Si/Al).sub.F                                                                           (%)       Vol (cc/g)                                                                            (cc/g)                                    ______________________________________                                        1        1.20     32        0.30    21.8.sup.b                                2        1.20     20        0.30    23.6.sup.b                                3        1.06     32        0.27    16.7.sup.b                                4        1.30     42        0.24    11.3.sup.b                                5        1.25     36        0.30    20.2.sup.b                                6        N/A 1.1.sup.a                                                                          25        0.25    11.1                                      7        N/A 1.4.sup.a                                                                          32        N/A     11.5                                      LiX Control                                                                            1.20     0         0.33    21.3                                      ______________________________________                                         N/A) not available                                                            .sup.a) from bulk elemental analysis                                          .sup.b) measured at 20° C., 1 atm                                 

Example 11. Predicted performance for O₂ VSA.

In order to evaluate the potential of the adsorbents of this inventionfor air separation, nitrogen and oxygen isotherms were measured for thematerial from 0 to 8 atm at 23° C. and 45° C. The data was then used ina global equilibrium model (GEM) which is routinely used as an indicatorof relative performance in adsorbent screening. This model is similar to"Flash" calculations in distillation (e.g., W. L. McCabe, and J. C.Smith, "Unit Operations in Chemical Engineering", 3rd edition, McGrawHill, New York (1976), p. 534). A key assumption in the model is thatthe mass transfer zones remain extremely narrow in each step of theprocess; i.e., zone-spreading due to mass-transfer resistances andisotherm-shape are taken to be negligible. As a first approximation,this is a reasonable assumption in the case of equilibrium-basedseparation processes. The omission of zone-spreading causes themodel-predictions to be, in general, over estimated but, the model hasbeen found to be good for relative performance-ranking. It is pertinentto note that the model satisfies mass and energy balances, andcalculates mixture adsorption using the Ideal Adsorbed Solution (IAS)theory (A. L. Meyers and J. M. Prausnitz, American Institute of ChemicalEngineers Journal, 11, 121 (1965) which is accepted for physicaladsorption of air on zeolites at ambient temperatures (G. W. Miller, K.S. Knaebel, and K. G. Ikels, "Equilibria of Nitrogen, Oxygen, Argon andAir in Molecular Sieve 5A" American Institute of Chemical EngineersJournal, 33, 194 (1987); and Srinivasan, R., Auvil, S. R., and Coe, C.G., "Tracer Pulse Chromatography for Measuring Equilibrium Adsorption inAir-Zeolite Systems", China-Japan-USA Symposium on Advanced AdsorptionScience and Technology-Extended Abstracts, Zhejiang University Press,China (1988)).

Table 2 below presents the gas capacities and predicted performance fromthe GEM model. Using the global equilibrium model the O₂ recovery andquantity of adsorbent required to produce a pound mole of O₂ product percycle (bed sizing factor) were calculated for a typical O₂ VSA process.We compared lithium X with the adsorbents described in Examples 1, 2,and 5 and found them to have similar properties.

                  TABLE 2                                                         ______________________________________                                        Predicted O.sub.2 VSA Performance                                             Gas Capacity (cc/g at                                                         23° C., 1 atm)                                                                       Predicted    Bed Size                                           Example                                                                              N.sub.2 O.sub.2                                                                              O.sub.2 Recovery (%)                                                                     Factor (× 10.sup.3)                    ______________________________________                                        1      18.6    3.8    62.6       14.2                                         2      25.6    4.7    63.3       12.6                                         5      16.4    3.4    61.0       16.5                                         LiX (1.2)                                                                            23.6    4.7    62.4       13.7                                         ______________________________________                                    

The results clearly show there is a utility for these adsorbents as airseparating agents.

The chemical composition of FAU/EMT zeolites, in their dehydrated statecorresponds to the following mole ratio of oxides: T₂ O:X₂ O₃:(2.0-4.0)SiO₂ in which T represents at least two cations selected fromLi⁺, Na⁺, tetramethylammonium, and optionally in addition K⁺. X isaluminum, gallium, boron or another trivalent element.

The synthesis of FAU/EMT zeolites can be performed from synthesismixtures with ratio's of reactants within the following ranges:

    ______________________________________                                                   broad range                                                                              preferred range                                         ______________________________________                                        OH/SiO.sub.2 1.0 to 6.0   1.5 to 4.0                                          SiO.sub.2 /X.sub.2 O.sub.3                                                                 2.0 to 6.0   3.0 to 4.6                                          T.sub.2 O/SiO.sub.2                                                                        0.5 to 3.0   0.75 to 2.0                                         H.sub.2 O/SiO.sub.2                                                                         15 to 100   20 to 50                                            ______________________________________                                    

The silica source may be aqueous sodium silicate solution, colloidalsilica, particulate silica, fumed silica and the like. Sources ofaluminum are sodium aluminate, aluminum sulfate, aluminum chloride,aluminum nitrate. Lithium, sodium, potassium and tetraalkylammoniumcations are introduced as hydroxides or salts.

There are three synthetic procedures for preparing the metallosilicatesof the present invention. In all procedures, an available recipe leadingto a FAU, EMT or FAU/EMT material is modified to enhance EMT formation.All recipes have in common that the synthesis mixture contains at leasttwo monovalent cations, most preferably selected from the group of Na⁺,Li⁺, tetramethylammonium and optionally, in addition K+.

The first procedure consists of modifying a synthesis gel that otherwiseleads to a FAU-rich and Al-rich zeolite (eventually contaminated withother zeolite phases such as LTA type) by adding foreign monovalentalkali metals or quaternary alkylammonium cations, as demonstrated inExample 3.

The second procedure consists of mixing two preaged gels. A first gelleading to an Al-rich FAU-rich phase, when crystallized separately(eventually contaminated with other zeolite phases such as LTA type),and a second aged gel leading to a Si-rich EMT-rich zeolite whencrystallized separately (e.g., ZSM-3, EMC-2), as demonstrated inExamples 1 and 2.

The third procedure consists of mixing a slurry of siliceous FAU/EMTintergrowth zeolite in its mother liquor with a preaged gel leading toan Al-rich FAU-rich phase, when crystallized separately (eventuallycontaminated with other zeolite phases such as LTA type), asdemonstrated in Example 4.

Below are some comparative examples provided in support of the claimeddistinctions over prior art compositions or methods.

Control 1: Synthesis using one aged gel, in presence of a mixture ofsodium and potassium.

The gel typically used for the synthesis of Al-rich FAU zeolite,prepared in Example 1 and having a composition: (Na₂ O)₄.34 (K₂ O)₁.45(Al₂ O₃) (SiO₂)₁.8 (H₂ O)₁₁₆ corresponding to an OH/SiO₂ ratio of 6.6was aged 40° C. for 47 hours and crystallized at 60° C. for 23 hours.The zeolite is separated from the mother liquor by centrifugation at4,000 rpm, washing and drying.

The product is a mixture of FAU and LTA zeolite types.

Control 2: Synthesis of low silica X.

A gel was prepared as explained for gel `C` of Example 8. To 44.1 g ofwater, 8 g of sodium hydroxide (Merck) and 6.12 g of 85% potassiumhydroxide (Merck) were added and dissolved. Subsequently, 4.85 g ofsodium aluminate (Riedel de Ha en) were added and dissolved until aclear solution was obtained. 12.3 g of water glass (Merck) were addedand the mixture stirred for 10 minutes. The gel has a molar composition:(Na₂ O)₅.3 (K₂ O)₁.8 (Al₂ O₃) (SiO₂)₂.2 (H₂ O)₁₂₂. It was crystallizedat 60° C. for 24 hours. The zeolite is separated from the mother liquorby centrifugation at 4,000 rpm, washing and drying. The product is apure FAU type of phase.

Control 3: Synthesis of zeolite X.

An amount of 5 g of sodium aluminate and 3.15 g of sodium hydroxide(Merck) are dissolved in 39 g of water. A solution composed of 18 gwater glass (Merck) and 26 g water was added. The gel has a molarcomposition: (Na₂ O)₃.6 (Al₂ O₃) (SiO₂)₃.0 (H₂ O)₁₄₄. It was stirred atroom temperature overnight and crystallized at 60° C. for 23 hours. Theproduct was recovered by centrifugation at 4,000 rpm, washing anddrying. It is identified as pure zeolite X.

The present invention has been set forth with regard to a number ofspecific examples. However, the full scope of the invention should beascertained from the claims which follow.

We claim:
 1. A process of adsorptively separating a more stronglyadsorbed gas from a less strongly adsorbed gas in a gas mixturecontaining a more strongly adsorbed gas and a less strongly adsorbedgas, comprising; contacting said gas mixture with a zone of adsorbentcontaining crystalline metallosilicate composition having an EMTstructure with a Si/X ratio of less than 2.0 and a lithium cationexchange of more than 80%, wherein X is selected from the groupconsisting of aluminum, boron and gallium, selectively adsorbing saidmore strongly adsorbed gas preferentially to said less strongly adsorbedgas, removing a gas containing said less strongly adsorbed gas anddepleted in said more strongly adsorbed gas from said zone andseparately removing said more strongly adsorbed gas from said adsorbent.2. The process of claim 1 wherein said EMT structure is in anintergrowth with a FAU crystalline structure.
 3. The process of claim 1wherein said zone is operated through a series of steps in a cyclicalmanner comprising; adsorption where said gas mixture contacts said zoneat elevated pressure to adsorb said more strongly adsorbed gas untilsaid adsorbent approaches saturation with said more strongly adsorbedgas and said gas containing said less strongly adsorbed gas and depletedin said more strongly adsorbed gas is removed as a product,discontinuing adsorption and desorbing said zone to remove adsorbed morestrongly adsorbed gas from said adsorbent to regenerate said adsorbent,repressurizing said zone with a gas rich in said less strongly adsorbedgas, and repeating said series of steps to conduct a continuous process.4. The process of claim 3 wherein said steps are conducted in aplurality of parallel connected adsorption beds as said zone whereinwhen one bed is conducting said adsorption another bed is beingregenerated.
 5. The process of claim 4 wherein said plurality of beds istwo parallel connected beds.
 6. The process of claim 1 where said morestrongly adsorbed gas is nitrogen.
 7. The process of claim 6 where saidless strongly adsorbed gas is oxygen.
 8. The process of claim 7 wheresaid gas mixture is air.
 9. The process of claim 8 wherein said gascontaining said less strongly adsorbed gas and depleted in said morestrongly adsorbed gas is at least 90% oxygen by volume.
 10. The processof claim 9 wherein said gas containing said less strongly adsorbed gasand depleted in said more strongly adsorbed gas is at least 93% oxygenby volume.
 11. The process of claim 1 wherein said contacting isconducted at a pressure in the range of 10 to 30 psia.
 12. The processof claim 1 wherein said separately removing is conducted at a pressurein the range of 0.1 to 7 psia.
 13. The process of claim 1 wherein insaid crystalline metallosilicate composition a remaining cation isselected from the group consisting of calcium, magnesium, zinc, nickel,manganese, sodium, potassium and mixtures thereof.